Looking at electrocatalysis at mesoscale

In the quest to develop technologies that can efficiently convert and store energy from electrochemical systems, scientists at the U.S. Department of Energy’s Argonne National Laboratory have designed new materials that can substantially improve the performance of the current state-of-the-art electrocatalysts.

In electrochemical systems such as electrolyzers, fuel cells and metal-air batteries, physicochemical processes that take place on electrodes that are responsible for the overall performance of these devices. Particularly, electrochemical reactions that involve oxygen represent the major obstacle in selection of materials that can be efficiently employed as cathode catalysts. Previous work on well-defined surfaces in the form of single crystals made of precious metals, principally platinum, showed great promise because of their effectiveness in reducing oxygen.

“Single crystals are ideal materials to obtain a fundamental insight into the processes that are controlling reaction rate,” said Argonne physical chemist and materials scientist Vojislav Stamenkovic. “We want to mimic their behavior in practical catalysts, but also reduce the cost by minimizing the amount of precious metals in the system.”

Stamenkovic saw the promise of investigating these materials at the mesoscale, which does not imply a specific length scale, but rather a principle of operating “in between” different physical regimes that exhibit unique functional behavior.

Stamenkovic and his colleagues developed thin-film-based materials with tunable structure, morphology and concentration profile. The team witnessed how individual randomly oriented nanoscale grains in the thin film coalesce and form large well-ordered facets without use of templates for epitaxial growth.

The interplay between the surface structure, domain size and functionality is represented by the distinct mesostructured morphology of the thin-film surfaces, which enables increased electrochemical activity without sacrificing surface area. Their electrocatalysts based on mesostructured thin film are 20 times more active than currently used conventional catalysts.

“The main issues with real-world catalysts are poor activity and durability and those issues must be solved before technologies are commercialized,” Stamenkovic said. “This new class of thin-film-based electrocatalysts has the potential to address those challenges.”

“Moreover, our thin film materials with altered structure have great promise to be employed in advanced batteries in which relationships between structure, function and composition are still largely unexplored,” said Nenad Markovic, who is an Argonne senior chemist and deputy director for science at the laboratory’s recently awarded energy storage hub.

This work has been published in Nature Materials and represents an initial study on mesoscale ordering in electrocatalysts, and Stamenkovic expects further advancement and optimization of the thin-film properties. Considering that mesoscale materials chemistry is still in its infancy, Stamenkovic believes that this field will open novel pathways in materials design.

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“Single crystals are ideal materials to obtain a fundamental insight into the processes that are controlling reaction rate,” said Argonne physical chemist and materials scientist Vojislav Stamenkovic.

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